1. Field of the Invention
The present invention relates to grain treatment systems and, more particularly, to an anti-coring, corner draw-off temperature conditioning system for select heating and liquid constituent control of grain through a heating medium comprising a mixture of condensible and non-condensible gases.
2. History of the Prior Art
The prior art is replete with grain treatment systems for improving the food value and animal digestibility. Many of these systems, incorporate steam chests and a process of direct contact heat exchange wherein the temperature of the heating medium is the single-most critical operational parameter. The contact is generally made between the substance to be heated and the products of combustion from a boiler, furnace or the like. In the case of grain treatment, steam from boilers is usually vented into the steam chest which comprises a vertical hopper through which the grain is allowed to fall. Steam injected into the bottom of the hopper rises to heat and moisturize the grain. Problems have arisen in the areas of proper temperature and time control as well as steam generation.
The prior art of steam chests extends into technological antiquity with steam utilized for heating tobacco leaves, grain, flour and animal feed. As stated above, grain used as animal feed is often treated with steam to improve its digestibility by the animal as well as food value. The steam which heats the grain is preferably injected into the grain immediately prior to feeding the animals to both heat it and raise the moisture level to around 24%. Generally the grain coming to the system is relatively dry often having between eleven and twelve percent moisture at ambient temperatures. Conventional steam system conditioning equipment raises the temperature of the grain as close as possible to approximately 190.degree. to improve commercially established digestibility characteristics such as starch availability. It is, of course, necessary to assure that none of the grain gets so hot so as to scorch it or break down the vitamin additives. Unfortunately with live steam, the maximum grain temperature rise that can be produced by a boiler system without producing a wet product is approximately 120.degree. F. An adequate boiler can thus produce 200.degree. F. grain only when the incoming grain is at or above 80.degree. F. At other times, and particularly in the winter, grain temperature of about 160.degree. F. to 180.degree. F. is the maximum. The amount of energy necessary to generate such quantities of steam are also of major concern.
Other prior art grain treatment systems have addressed the need for moisture control with apparatus which introduces steam and air in combination. For example, U.S. Pat. No. 1,185,622 to Boss teaches a 1916 process of conditioning food forming substances. The Boss patent sets forth the moisture treatment of grain or the like in such a manner that it is hydroscopically conditioned by either adding or taking moisture from such particulate matter. These systems are useful in preparing the grain to a condition where it is uniformly hydrous in its character. Such product is more thoroughly digested in given quantities, in shorter time and with greater nutritive and body building effect. It has thus been a goal in the prior art grain condition technology to provide a treating "fluid" and system therefor capable of delivering or withdrawing moisture or other substance to or from the material to be acted upon for swelling or shrinking or wetting or drying the material as needed. To affect this end result, air and steam have been utilized in various heating and flowing configurations such as that initially shown in the Boss patent. This prior art does not envision heating the grain to a controlled higher temperature so as to cook it for better digestibility. More importantly, it does not envision the functional problems of handling the grain efficiently with more advanced technology.
More advanced prior art grain treatment technology in steam chests have generally included refinements on the age old principle of steam moisturizing. For example, U.S. Pat. No. 1,574,210 to Spaulding teaches a method and apparatus for steaming grain and the like. A steam chest is thus taught. The Spaulding steam chest utilizes gravity descent and angularly disposed baffles for deflecting the grain. Steam supply ports are provided for the steaming operation of the grain during its descent. A prior U.S. patent issued to Henson under U.S. Pat. No. 1,174,721 sets forth an improved method of supplying moisture to grain and the like by utilizing the flow of steam and air heated by said steam prior to entry into a treatment chamber. Moisture is added to the grain by introducing steam with the air prior to entry into the treatment chamber. The Henson patent further teaches the use of a hygrometer to determine the moisture content of the air. Grain which is fed into the interior of the mixing treatment chamber comes in contact with the vapor which tends to condense thereupon. In this manner, the amount of moisture deposited in the substance passing through the treatment chamber may be calculated from the data given. Such a system will also work with raw steam being used instead of the mixture of steam and air.
These prior art steam chest systems have been shown to be effective for removing or adding moisture to grain. Unfortunately, many problems exists such as grain clinging, bacterial residue, heat loss after shut-down, and particularly coring in conventional steam chest structures. The degree of heat and moisture contributed to the grain is also generally hard to control and/or define in any empirical manner short of raw data measurements such as that discussed above. Conventional prior art systems simply do not prevent coring and the problems recited above, nor do they envision control of heat added to the grain or the time in which the grain is exposed to the heat, as discussed below.
Conventional steam chest grain processing vessels are generally fabricated from planar sheet metal into rectangular units adapted for receiving grain therein. Steam is injected in the lower regions of the steam chests and allowed to percolate up through the descending grain. The grain flow system is generally regulated by a lower discharge port in a lower region of the vessel. The discharge region is preferably tapered and a continuous grain feed is provided therefrom. A myriad of problems prevail with such structures, including the fragility of the overall steam chest and the grain treatment efficiency therein. The planar walls generally do not provide sufficient structural strength to permit pressurization of the steam chest which is often necessary for elevating grain temperatures during processing therein. Moreover, the rectangular configuration creates four corner regions which are by definition outwardly of any symmetrically tapered grain discharge area. For this reason grain within the corner regions of the steam chests are inhibited from flow therein. Traditional laminar flow equations may be applied in conjunction therewith to mathematically explain the phenomena of "coring" within such steam vessels. Coring is produced when the grain adjacent the side walls and in the corners of the steam chests stacks in place and forms a central tunnel therethrough where the grain falls. Generally the central core where the grain funnels through is circular in cross-section and of a diameter much less than that of the steam chests. In fact, flow areas of 25-30% of the overall cross-sectional area of the steam chest is not unusual.
Aside from flow problems in conventional steam chests as described above, accumulation of packed grain in the side and corner regions of the vessel produces a second equally serious problem. Steam percolating up through the steam chest is absorbed by the stagnating grain therein, further enhancing the sticking and jam configuration thereof as well as inducing the growth of bacteria from the moisture and heat imparted thereto. During shut down of the operation at the end of an operation cycle, the grain is left within the steam chest for further bacterial growth and cooling of the steam chest itself. Because of the moisture laden grain, conductive cooling to the side walls of the vessel is greatly expedited necessitating more energy for start up operation in the next cycle. For example, steam chests which cool to ambient during the night period will require almost twice as many btu's for start up than a steam chest whose temperature only drops a few degrees during the shut down period. Such a steam chest having improved heat retention characteristics can substantially reduce the operational costs in grain processing. Moreover, steam chests capable of continuous scouring of the sides to eliminate any sticking or residual grain therein would eliminate the wet, conductive cooling of the steam chest during the shut down period as well as the growth of bacteria therein. Bacterial growth also affects not only the stagnant grain but grain passing therethrough which is exposed to the stagnant side wall sections. Contamination is thus a third factor in the design consideration of such units.
Aside from steam chest systems, more advancement in technology has addressed the issue of control of various aspects of the steam itself in steam systems. These aspects include both the adding of moisture to and removal of moisture from particulate matter of a general nature. For example, U.S. Pat. No. 4,024,288 issued to Witte illustrates a method of treating particulate matter for conditioning oil containing vegetable raw materials. In the Witte patent, air and steam are again utilized for the treatment of the raw material. The utilization of super-heated steam coming from a heat exchanger which is then mixed with air is set forth and shown in the Witte reference and discloses an effective means for immersing the raw material into a steam and hot air bath. Material leaving the bath is then dried by air issuing from a hot air heat exchanger. While effective in heating by means of steam, Witte maintains little control over the temperature to which the raw material is heated and requires two separate fluid streams to attain the desired temperature and moisture levels. This system is not particularly adapted for addressing the "functional" problems set forth above for grain steam chests. U.S. Pat. No. 4,249,909 issued to Comolli is yet another technological advancement which sets forth a staged process for drying wet carbonaceous material. The staged drying procedure permits wicking up of hydrocarbons contained in coal to seal the surface of dried coal products sufficient to prevent appreciable reabsorption of moisture and consequent heating and spontaneous ignition. The Comolli procedure was developed for this particular application and in so doing manifested the advances made in the state of the art in steam treatment systems. These advances may be seen in part in the efforts to define and control various parameters of steam such as partial pressures. The pressures exerted by each constituent alone in the volume of a mixture at the temperature of the mixture are called partial pressures. The partial pressure is directly related to the mole fraction of a constituent present in a mixture and the total pressure thereof. However, to control partial pressure it is necessary to provide an adequate treatment chamber which evenly distributes and conditions the grain passing therethrough. These aspects are set forth above and comprise the critical difference between acceptable and unacceptable steam chest systems.
It may thus be seen that the treatment of grain in steam chests has been an area of marked technological evolution through the years. The advantages of steam as a moisturizing and heating medium for other food stuffs as well as grain may likewise be useful if the end product can be selectively controlled. Conventional treatment processes for cellular matter such as grain generally use raw steam as a sole element of a heating medium or in combination with air or similar non-condensible gases for the moisturizing process. As stated above, such processes are typically incapable of effectively treating the grain in the precise manner necessary for maximum utilization and adequate grain "stagnated" and "coring" control. For example, specific moisture levels, heat absorption and final grain temperatures must be obtained in a uniform fashion for reliable and effective conditioning. Reasons for the inability of conventional apparatus to meet such demands of the market are due to their inability to evenly and homogeneously process a given quantity of grain whereby each section of grain is treated for an equal time to a select condition.
Most conventional grain treatment systems incorporate a tank wherein grain is allowed to funnel downwardly through a central aperture or gate. Steam pipes are inserted into the tank body and steam discharged therefrom is utilized to heat and moisturize the grain funnelling therethrough. Unfortunately, the passage of grain within the tank is not uniform and, in fact, tends to core down the center as discussed above. The grain is therefore, not homogeneously treated by the injected steam and grain stagnation results. The treatment tank is thus an integral element of appropriate grain processing and conventional technology has generally not addressed appropriate steam or grain flow controls therethrough.
The prior art systems as shown in the aforesaid patents which permit a flow of unpacked grain to be channelled through a series of baffles is not generally commercially utilized due to the vast quantities of grain being treated and operational constraints associated therewith. Grain is generally carried by box cars and conveyors belts in large volumes which quickly fill treatment vessels utilized for temperature conditioning. The fact that the grain fills the vessel has not been deemed to be a critical problem in the temperature treatment thereof. This is not the case. The flow patterns of grain funnelling and coring through such tanks generally prevents homogeneous grain treatment. When a column of grain is flowing vertically downward in a steam chest or holding bin, the grain along the walls will tend to slow down due to friction at the wall. The stacking of the grain can, in some instances, show a "bridging" effect which greatly slows the movement near the walls and speeds movement in the center for a given average grain flow rate. Also, the grain will tend to form a moving column in the middle if the opening at the bottom is smaller than the steam chest itself. For example, a central aperture at the lower end of a hopper or tank only allows grain situated in the central region of the tank to fall first. The grain around the outside walls thereof generally fall in on top of the funnel of grain passing therebeneath. As new grain is inserted into the tank, it also falls down through the center leaving the grain situated along the side walls to prolonged exposure in the steam within the tank. This grain becomes moisture laden and prone to bacterial growth. The grain funnelling through the central region thereof is, likewise exposed to this bacteria and is treated for a short period of time by the steam injected therein. Therefore, the type of heat treating fluid as well as the processing vessel are critical elements of an homogeneous and effective grain treatment system.
It would be an advantage therefor to overcome the problems of the prior art by providing a system for select temperature and moisture conditioning of grain by an effective heating medium injected into a processing vessel which uniformly carries grain therethrough without coring. The system of the present invention affords such an operation by utilizing a vapor generator, or the like, in conjunction with an upstanding vessel having grain discharge means disposed therein for uniformly passing homogeneous plugs of grain therethrough and simultaneously scouring all interior surfaces and all corner regions therein (i.e. corner draw-off). The amount of heat and moisture supplied to the grain may therein be controlled by the rate of fuel burning of the vapor generator or by pressurization, while the time the grain is exposed thereto may be controlled by the time in which the grain is allowed to pass through the vessel. More food value can thus be supplied in the grain with less energy expended in steam generation.